UberTuber

[DLW]

Hello,

I'm having trouble with my UberTuber build. It passes sound, but sounds muffled/awful. I followed the BOM without knowingly making any modifications. The resistors and capacitors were all checked with a multimeter immediately before placing the component on the board. The volume knob and boost switch seem to do something. The other knobs don't seem to do much. The plate voltages (T1 and T2 below) are abnormally high, which suggests this is the problem. Unfortunately, I don't really know how to read a schematic to figure out which parts could be causing the issue. Any and all help is greatly appreciated!

Solder side:

Component side:


Test box voltage = +18.09
T1 = +17.54
T2 = +17.37
T3 = +11.5
T4 = +6.47

Thanks!
Darin

[madbean]

Your plate and cathode resistors are correct. Your heater voltage is slightly high at 6.47v but that may not be a concern. The bad plate voltages may indicate an issue with the tube itself. Please link to where you purchased it.

[DLW]

I bought this one... https://www.ebay.com/itm/NOS-6111-dual-triode-subminiature-vacuum-tubes/290862897028?ssPageName=STRK%3AMEBIDX%3AIT&_trksid=p2057872.m2749.l2649

[madbean]

I bought this one... https://www.ebay.com/itm/NOS-6111-dual-triode-subminiature-vacuum-tubes/290862897028?ssPageName=STRK%3AMEBIDX%3AIT&_trksid=p2057872.m2749.l2649

Hmm. There's no branding on the tube and the listing does not indicate a manufacturer. How about on the actual tube you received? Is there a company name or any other writing on it besides 6111?

[DLW]

The writing is on the bottom side of the tube :|

This is what I can read:  6111..66404

I'll contact the seller to ask for more info about the tubes.

[DLW]

I finally heard back from the eBay seller...they have no idea who manufactured the tubes. Probably not the highest quality. Does it make sense to replace the tube? Is there a way to test a tube before it goes on the board? I'm not even sure that I didn't damage it while soldering. Are these tubes easy to damage that way?

[BrianS]

I purchased my tube from the same place and my build is working.  Not saying that your tube is good, just saying mine was ok. 

Well disregard that. I plugged mine in and it worked then I remembered I needed to set the trimmer.  My voltages are running the same as yours.  This can't be a coincidence that my voltage at T1 and T2 are almost the same.  I'm pulling mine and getting another one from a reputable place. 

[DLW]

That's good to know. The seller was actually very reasonable and responsive. I don't blame him at all. I just ordered a Raytheon tube. Only 4 dollars more than the no name brand. Maybe that will fix it...

[BrianS]

Please post your outcome.  Thanks.

[DLW]

Genuine Raytheon tube fixed it. Pedal is fully operational now. Thanks for the help.

[madbean]

That's great to hear. Thanks for the update.

[EBK]

I'm going to tag onto this thread to ask if the following voltages are ok:
V+: 17.97V
T1: 15.28V
T2: 13.07V
T3: 11.59V
T4: 6.34V

T1 and T2 are a bit high, no?
Tube from Smallbear.

I'll also note that SAT and CUT do not seem to make noticeable changes to the sound.  Although LVL and DRV make it louder or quieter, things seem to be staying fairly clean sounding.

[EBK]

I have no real experience analyzing tube circuits, but here is a somewhat reckless wild guess as to what's going on in my build:

With my higher plate voltages, are my triodes operating at lower than expected gain, resulting in my cleaner than expected sound, with a signal not high enough to push the second triode very hard and failing to clip noticeably at the saturation control?

[madbean]

T2 is a bit high but not too worrisome. T1 is a problem though. I start by increasing the plate resistor on that one from 100k to 150k. You could lower T2 by increasing its resistor to 120k. Your V+ and heater are spot on so it's just wrangling those plates in.

Maybe for the next batch I should put trimmers in place of resistors for the plates. I never really had a problem with my own set of tubes achieving proper bias but of course people are getting them from all over the place. So, it seems like an obvious improvement to the design.

[BryGuy]

My voltage are off as well. Everything seemed to be working as far as I could tell. Haven't had a chance to box mine up yet. I'll see if I can get the voltages posted when I get a chance.